The present invention relates to chromium ion doped complex optical material for enhanced infrared fluorescence emission and a using method thereof. Particularly, the present invention relates to complex optical material that trivalent (+3) ytterbium ion and tetravalent (+4) chromium ion are codoped as active media into single crystalline, poly crystalline or amorphous material and relates to a using method thereof in which the media are not excited at the range between 600 nm and 800 nm wavelength but at the wavelength band of about 980 nm. At the former wavelength range, excited-state absorption is occurred in the chromium ion, but at the latter wavelength, absorption is strongly occurred in the ytterbium ion. The optical material of the present invention can be applied to solid-state lasers, optical amplifiers and the likes. When excitation is occurred in the optical material at the wavelength band, the energy is transferred from the ytterbium ion to the chromium ion to produce fluorescence in the band between 1200 nm and 1600 nm wavelength. Therefore, the efficiency of fluorescence emission can be enhanced.
Chromium ion has several oxidation numbers and is the stablest in trivalent (+3) state among the oxidation states. It has been known lately that the tetravalent (+4) state can be stably formed in crystalline and glass system.
Particularly, U.S. Pat. No. 4,932,031 discloses solid-state laser consisted of chromium doped single crystalline medium and a resonance oscillator operating in the range between 1150 nm and 1350 nm wavelength.
U.S. Pat. No. 4,987,575 also discloses a laser operating in the infrared region of 1xcx9c2 micron and tetravalent chromium ion doped laser material. As stable tetravalent chromium ion doped crystalline material, the patent suggests olivine-like structure of (A) (RE)GeO4 (wherein, A is Na or Li, RE is Y, La or Gd) or willemite structure of Zn2(Si or Ge) O4.
Meanwhile, as stable tetravalent chromium ion doped amorphous material, CaOxe2x80x94Al2O3xe2x80x94MgO and CaOxe2x80x94Al2O3xe2x80x94SiO2 systems have been published.
U.S. Pat. No. 5,119,382 also discloses a new Q-switch using tetravalent chromium ion doped crystalline material.
U.S. Pat. No. 5,717,517 also discloses a polymer optical fiber amplifier in which fine crystalline containing tetravalent chromium or trivalent vanadium ion is dispersed.
However, the fluorescence lifetime of near infrared wavelength emission of the tetravalent chromium ion doped materials is very short (See, K. Cerqua-Richardson, et al., xe2x80x9cSpectroscopic Investigation Cr4+-Doped Glassesxe2x80x9d, OSA Proceedings on Advanced Solid-State Lasers, 13, pp 52-55 (1992)). Excited-state absorption also occurs in the wide wavelength range of 600xcx9c800 nm. In the wavelength band between 600 nm and 800 nm, ground-state absorption strongly occurs. However when excitation occurs in the wavelength band, the efficiency of laser may be deteriorated due to the excited-state absorption (See, N. V. Kuleshov, et al., xe2x80x9cExcited-state absorption and stimulated emission measurements in Cr4+:forsteritexe2x80x9d, Journal of Luminescence, 75, pp 319-325 (1997)).
It is, therefore, an object of the present invention to provide chromium and ytterbium ion codoped complex optical material, which can increase the excitation efficiency and thereby enhancing the fluorescence emission intensity in the infrared wavelength range.
It is another object of the present invention to provide a using method of complex optical material, in which the fluorescence emission efficiency can be enhanced by using the optical material with exciting the media in the absorption wavelength band of the ytterbium ion. That is, the present invention is to enhance excitation efficiency of tetravalent chromium ion by using the trivalent ytterbium ion which is long in fluorescence lifetime and has large absorption cross-section in the narrow wavelength centered at xcx9c980 nm. In the present invention, the energy is not directly absorbed by the chromium ion, but by the ytterbium ion and then is transferred from the ytterbium ion to the chromium ion to emit fluorescence.
In accordance with one embodiment of the present invention, there are provided complex optical material that trivalent ytterbium ion is codoped into single crystalline, poly crystalline or amorphous material using tetravalent chromium ion as an active medium.
Here, it is preferable that the concentration of the ytterbium ion should be larger than that of the chromium ion in the material. More preferably, the chromium ion is doped with the amount between 0.01 mol % and 0.1 mol %, the ytterbium ion is codoped with the amount between 0.05 mol % and 2 mol %, and the amount of the ytterbium ion is 5 to 200 times more than that of the chromium ion. Most preferably,the amount of the ytterbium ion is 20 to 100 times more than that of the chromium ion.
The complex optical material may be used for laser resonance oscillators, saturable absorbers, optical fiber amplifiers, planar waveguide amplifiers or the likes.
The complex optical material produces fluorescence in the range between 1200 nm and 1600 nm wavelength.
In the complex optical material, the absorption wavelength band of the ytterbium ion is used as excitation wavelength. Here, among the absorption wavelength band, the preferable wavelength range is between 850 nm and 1050 nm, and the more preferable wavelength range is between 970 nm and 990 nm.
Meanwhile, the chromium ion may be replaced by trivalent (+3) vanadium ion.